Generally, a letter or object is placed in an envelope, mail receiver and sender information is written or printed on the front of the envelope, and the envelope is then sealed by using glue or other ways. However, general envelopes have been used for a long time without changing a lot; they are only changed a little in style, for example, a metal fixing sheet or cotton winding fastener may be added in a seal structure of a envelope, or a self adhesive glue is attached on an envelope seal. Therefore, a conventional envelope cannot be adjusted with a different content.
For the cushioning protection of a content, the content will first be wrapped in a plastic film with a plurality of small air sacs and then placed in an envelope, or the plastic film with a plurality of air sacs is laid in the envelope in advance and the content is then placed in the envelope, thereby avoiding the damage of the content due to a direct impact through the cushioning protection of the small air sacs. However, the shock-absorptive capability of the small air sacs is limited; they cannot achieve cushioning shock-absorption with respect to a larger impact load. Obviously, a precise object needing a more perfect protection during transportation cannot be mailed with this kind of package. Additionally, a conventional pack bag with cushioning function is disclosed in Japanese utility model publication 4-121273 and includes a plurality of air-sealed bags within the pack bag structure; the air-sealed bags does not communicate with each other so that when one of the air-sealed bag is damaged with the air inside being released, other air-sealed bags can still function normally. Nevertheless, the conventional pack bag fails to provide a function for the object inside the pack bag from escaping out.